Dehydration, Micellization, and Phase Separation of Thermosensitive Polyoxazoline Star Block Copolymers in Aqueous Solution [component]

Suitably end-functionalized diblock copolymers (2-isopropyl-2-oxazoline)-b-(2-ethyl-2-oxazoline) (PIPOZ-b-PEOZ) were linked to a tetrafunctional core in order to synthesize two isomeric thermosensitive 4-arm star block polymers which have the PIPOZ block near the core, core-(PIPOZ-b-PEOZ)4, or near the outer surface the star polymer, core-(PEOZ-b-PIPOZ)4. The solution properties of the star copolymers in water were monitored by turbidimetry, microcalorimetry, and small-angle X-ray scattering
more » ... XS). The dehydration and cloud-point temperatures of both core-(PIPOZ-b-PEOZ) 4 and core-(PEOZ-b-PIPOZ) 4 in water are in the vicinity of 50 C. Above this temperature, core-(PIPOZ-b-PEOZ)4 forms star-like aggregates, whereas core-(PEOZ-b-PIPOZ)4 remains isolated, with no sign of aggregation. These results demonstrate the importance of chain architecture on the association of thermosensitive tetra-arm star block copolymers in water above the solutions phase transition temperature. PIPOZ and PEOZ are soluble in water below ca. 45 C. The PIPOZ chains dehydrate between 45 and 55 C, while PEOZ remains soluble in water, hence PEOZ-b-PIPOZ copolymers are amphiphilic in this temperature range. Above 55 C, both PIPOZ and PEOZ are dehydrated and insoluble in water. It was observed experimentally that at 50 o C PEOZ-b-PIPOZ aggregation occurs with concomitant macroscopic liquid-liquid phase separation, whereas at 70 o C phase separation occurs without macroscopic phase separation. Using PEOZ-b-PIPOZ diblock copolymers, we prepare via click coupling two isomeric tetra-arm star copolymers, [core-(PIPOZ-b-PEOZ)4], in which the PIPOZ blocks are linked directly to the core, and [core-(PEOZ-b-PIPOZ)4], in which the PEOZ block is linked to the core (cf. Scheme 1). These two star block copolymers were utilized to investigate the architecture dependences of the micellar structure as well as the dehydration and phase Scheme 1. Synthesis of of core-(PEOZ-b-PIPOZ) 4 and core-(PIPOZ-b-PEOZ) 4 starting from the tetrafunctional moiety core-4-yne. EXPERIMENTAL SECTION Materials. All chemicals were purchased from Sigma-Aldrich Chemical Co. and used as received unless specified otherwise. 2-Isopropyl-2-oxazoline was synthesized from isobutyronitrile and 2-aminoethanol according to the synthetic protocol of Huber and
doi:10.1021/acs.macromol.8b02528.s001 fatcat:rhjretbrpvbs7fj3ip42kajn6y